Prepolymer crystallization and solid phase polymerization



United States Patent 3,390,134 PREPOLYMER CRYSTALLIZATION AND SOLIDPHASE POLYMERIZATION Charles Jacob Kibler, Kingsport, Tenn., assignor toEastman Kodak Company, Rochester, N.Y., a corporation of New Jersey NoDrawing. Continuation-impart of application Ser. No. 259,370, Feb. 18,1963. This application Jan. 16, 1967, Ser. No. 609,322

Claims. (Cl. 260-75) ABSTRACT OF THE DISCLOSURE An improved solid phasepolymerization process for building up the molecular weight of a linearpolyester containing branched chain alkylene radicals, said improvementcomprising, prior to build up, the preliminary crystallization in avolatile liquid (e.g., acetone, aqueous acetone, tetrachloroethane,methanol, ethyl acetate, etc.) of a prepolymer of said linear polyestercontaining branched chain alkylene radicals.

This application is a continuation-in-part of Kibler U.S. Ser. No.259,370, filed Feb. 18, 1963, now abandoned.

This invention relates to an improved solid phase, vacuum-typepolymerization process for rapidly building up the molecular weight of alinear polyester so as to attain an inherent viscosity of at least 0.7,said linear polyester containing branched chain alkylene radicals. Inone of its more specific aspects, this invention relates to an improvedsolid phase, vacuum-type polymerization process wherein the improvementcomprises the preliminary crystallization of a prepolymer of said linearpolyester, said prepolymer being in the form of particles.

Solid phase, vacuum-type polymerization processes are well known in thepolymer art. Examples of prior art which discuss this process includeFrench Patent 1,081,- 457, U.S. Pa ent 2.518,283, U.S. Patent 2,901,466,and U.S. Patent 2,921,052.

Linear polyesters containing branched chain alkylene radicals are alsowell known in the polymer art, as illustrated in the above-cited patentsas well as in U.S. Patent 2,744,092, etc. It is, therefore, quiteobvious that those skilled in the art need no elaborate explanation ofhow to prepare linear polyesters containing branched chain alkyleneradicals, prepolymers thereof, or how to conduct a solid phase,vacuumtype polymerization process.

However, the prior art recognizes that it is sometimes diificult toapply the solid phase polymerization process to prepolymers containingbranched chain alkylene radicals. Therefore, there is a need in thepolymer industry for an improvement in the solid phase process to enableit to be advantageously applied to this type of prepolymer.

It is an object of this invention to provide an improved solid phase,Vacuurn-type polymerization process for rapidly building up themolecular weight of a linear polyester containing branched chainalkylene radicals.

It is a further object of this invention to provide an improved solidphase, vacuum-type polymerization process for obtaining linearpolyesters containing branched chain alkylene radicals and having aninherent viscosity of at least 0.7.

Other objects of this invention will appear herein.

These and other objects are obtained through the practice of thisinvention, at least one embodiment of which comprises the process of (l)mixing particles of a prepolymer of a linear polyester containingbranched chain alkylene radicals with a volatile liquid; (2) separatingsaid volatile liquid and said prepolymer particles when 3,390,134Patented June 25, 1968 said particles have become characterized by ahigh degree of crystallization; and (3) heating said crystallized pre'polymer particles in an enclosed polymerization zone under a vacuum atfrom 5 C. to C. below their melting point, whereby a linear polyesterhaving an inherent viscosity of at least 0.7 and also at least 0.3 unitgreater than for the prepolymer is obtained within about three hours ofcommencing said heating in said enclosed polymerization zone.

Through practice of the above-described embodiment of this invention,one can obtain highly advantageous properties for linear polyesterscontaining branched chain alkylene radicals. This is contrary to sometheoretical considerations which have been advanced indicating thatsolid phase polymerization of a prepolymer could be more effectivelyconducted without any preliminary crystallization, or that no advantagewould be derived from such a treatment.

The inherent viscosities mentioned in this application were determinedby means of measurements at 25 C. employing 0.25 percent, by weight,concentrations of polymer dissolved in a solvent composed of 60 percentphenol and 40 percent tetrachloroethane.

In regard to the linear polyesters which can be employed in the practiceof this invention, various patents can be referred to for details inpreparing them and their prepolymers. For example, U.S. Patent2,901,466, describes the preparation of prepolymers of linear polyestersprepared from terephthalate constituents, 1,4-cyclohexanedimethanol, andvarious branched chain glycols. These constituents can be modified bythe presence of other constituents. U.S. Patent 2,727,882, describes thepreparation of prepolymers wherein the acid constituent is terephthalicacid, In addition, U.S. Patent 2,744,089, discloses the preparation ofprepolymers wherein the acid constituent is 4,4'-sulfonyldibenzoic acid.Other references listed hereinabove should also be referred to fordisclosures relating to prepolymer preparation.

The prepoylmer particles encompassed by this invention have an inherentviscosity of from about 0.1 to about 0.40 and may be made by grindingsolid prepolymers to to form particles which substantially completelypass a 20-mesh screen with less than 25 percent passing a 200- meshscreen. The screen mesh sizes mentioned here and elsewhere in thisapplication are based upon the U.S. Sieve Series.

The mixing of the prepolymer with a volatile liquid in accordance withthis invention effectuates a change in the prepolymer from an amorphousform to a form which has a high degree of crystallinity. By the termvolatile liquid I mean a liquid which has a boiling point of C. orbelow. The volatile liquid used in the preliminary crystallization stepincludes both solvents and nonsolvents for the particular prepolymer.The use of nonsolvents is permitted since, in a number of cases, thereis no actual dissolving of the prepolymer particles. The use of either asolvent or a nonsolvent produces distinct advantages over the use of theother. Examples of liquids which can be employed here include alcoholshaving 1 to 15 carbon atoms, alkyl alkanoates having 1 to 15 carbonatoms, ketones having 1 to 15 carbon atoms, chlorinated hydrocarbons,etc. The volatile liquid may be a combination of one of theabove-enumerated liquids and water to the extent that no more than about75 percent by weight of the combination is water. The presence of wateris permissible in order to reduce the hazards of fire or breathing toxicvapors from some volatile liquids.

Preferred volatile liquids are tetrachloroethane, perchloroethylene,methylene chloride, carbon tetrachloride, chloroform, aqueous acetone(of which mixture 25-75 percent by weight is water), anhydrous acetone,methanol, ethanol, isopropanol, butanol. aqueous methanol, aqueous Items1 through 4 on the following table will serve to further illustrate theinvention by means of certain embodiments although it is to beunderstood that such illustrations and the preferred methods discussedabove are not intended to limit the scope of the invention unlessspecifically indicated elsewhere herein. Items 5, 6, and 7 are presentedfor purpose of comparison in order to show the advantages of theinvention.

EFFECT OF CRYSTALLIZATION ON THE VISCOSITY OBTAINED IN SOLID PHASEPOLYMERIZATION AT 0.08 MM. Hg PRESSURE Polyester Composition InherentViscosities Propolymer Build-Up Obtained Acid Components GlycolComponents Inherent Conditions Viscosity Not Crys- Crystal 1st 2nd 1st2nd Time Temp. tallized lizcd (Hr.) C.

1 Neopentyl 0.21 6 270 0.32 0.75 2 d 0.17 3 270 0.31 1.09 3 d 0. 24 3270 0. 42 1. 26 4 0.16 .5 250 0.20 0. 95 5 0. 31 3 230 1. 02 1. 05 6 TCHD t 0. 30 3 260 1. l0 1. 7 T 83 B 17% CHDM 0. 31 3 240 1 23 1. 29

S=4,4Sullonyldibenzoic Acid; T=Terephthalie Acid; I=Isophthalie Acid; 13Sebacic Acid.

be measured by various means, such as X-ray diifraction, density,melting point, etc. In addition, the crystallization of the prepolymermay be accelerated by stirring the mixture at room temperature for onehour to several days. The stirring time may be decreased to as little asfive minutes if higher temperatures are employed.

It a solvent for the prepolymer is used as the volatile liquid, theprepolymer may be allowed to either completely or partially dissolve,after which the crystallized prepolymer may be obtained by adding aprecipitant such as an alcohol (e.g., butanol, etc.), a ketone (e.g.,acetone, etc.), or other similar precipitant. Alternatively, the solventcan be evaporated to obtain the crystallized prepolymer. After treatmentwith either a solvent or nonsolvent, the prepolymer is dried beforeintroducing it into the solid phase, vacuum-type polymerization process.

The branched chain alkylene radicals of the linear polyester usable inthis invention may be present as a par of either the acid constituent orthe glycol constituent or both. Examples of acids and glycols containinga branched chain alkylene radical are disclosed in various patents,among which is the above-cited Kibler et al. US. Patent 2,901,466.Preferred such acids include a-ethylsuberic acid, a,u'-diethyladipicacid, dimethylmalonic acid, and ethylbutylmalonic acid. Preferred suchglycols include 2,2-dimethyl-l,3-propanediol (neopentyl glycol),2-methyl-1,5-pentanediol, and 2,2,4-trimethyl-l,3-pentanediol.

The linear polyesters of this invention melt at from about 150 C. toabout 300 C. and are those of constituents (A) at least one difunctionaldicarboxylic acid, at least 50 mole percent of said acid constituentbeing an acid having two carboxyl radicals attached to a hexacarbocyclicnucleus, and (B) at least one glycol, wherein at least 50 mole percentof said acid and glycol constituents have a branched chain alkyleneradical.

The especially advantageous and surprising results of this invention areachieved by using the volatile liquid treatment process described aboveand more specifically illustrated by the following preferred methods.

METHOD I A mixture of six liters of acetone and six liters of water in a22 liter flask was stirred rapidly as six kg. of a pulverized prepolymerwas added. This mixture was stirred for 24 hours at room temperature.The solid was filtered and dried.

METHOD II Same as Method I except that 100 percent acetone was used. Inthis case, it may be necessary to regrind the prepolymer as it may tendto become a congealed mass before thoroughly crystallized.

The prepolymers which are set forth in the above table were prepared bythe process described in US. Patent 3,075,952 granted on Jan. 29, 1963,to Coover et al. who are coworkers in the same laboratories of the sameassignee as the present inventor. The prepolymers were ground to formparticles which substantially completely pass a 20-mesh screen with lessthan 25 percent passing a 200mesh screen. The samples of powder whichwere crystallized so as to illustrate this invention were treated byMethod I in the case of Item 1 and by Method 11 as to the other items inthe table which illustrate this invention.

As is apparent from the preceding disclosure, this invention provides anew and useful process for preparing a linear polyester of constituents(A) at least one difunctional dicarboxylic acid, wherein at least 50mole percent of said acid constituent is an acid having two carboxylradicals attached to a hexacarbocyclic nucleus and (B) at least oneglycol, wherein at least 50 mole percent of said acid and glycolconstituents have a branched chain alkylene radical, said linearpolyester having an inherent viscosity in a mixture of 60 percent phenoland 40 percent tetrachloroethane of at least 0.7 and melting at fromabout 150 C. to about 300 C., said process comprising:

(1) mixing one part by Weight of particles of a prepolymer of saidlinear polyester, said prepolymer having an inherent viscosity of fromabout 0.1 to about 0.40, which particles substantially completely pass a20-mesh screen with less than 25 percent passing a ZOO-mesh screen, withfrom about 2 to about 25 parts by weight of a volatile liquid composedof (a) up to 75 percent by weight of water and (b) a compound selectedfrom the group consisting of alcohols having 1 to 15 carbon atoms, alkylalkanoates having 1 to 15 carbon atoms, ketones having 1 to 15 carbonatoms, and chlorinated hydrocarbons,

(2) separating said volatile liquid and said prepolymer particles whensaid particles have become characterized by a high degree ofcrystallinity, and

(3) heating said crystallized prepolymer particles in an enclosedpolymerization zone under a vacuum at from 5 C. to C. below theirmelting point, whereby a linear polyester having an inherent viscosityof at least 0.7 and also at least 0.3 units greater than for theprepolymer is obtained within about three hours of commencing saidheating in said polymerization zone.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variations and modifications can be effected withoutdeparting from the spirit and scope of the invention as describedhereinabove and as defined in the appended claims.

I claim:

1. A process for preparing a linear polyester of constituents (A) atleast one difunctional dicarboxylic acid,

wherein at least 50 mole percent of said acid constituent is an acidhaving two carboxyl radicals attached to a hexacarbocyclic nucleus and(B) at least one glycol, wherein at least 50 mole percent of said acidand glycol constituents have a branched chain alkylene radical, saidlinear polyester melting at from about 150 C. to about 300 -C., saidprocess comprising:

(1) mixing one part by weight of particles of a prepolymer of saidlinear polyester, said prepolymer having an inherent viscosity of fromabout 0.1 to about 0.40, which particles substantially completely pass a20-rnesh screen with less than 25 percent passing a ZOO-mesh screen,with from about 2 to about 25 parts by weight of a volatile liquidcomposed of (a) up to 75 percent by weight of water and (b) a compoundselected from the group consisting of alcohols having 1 to carbon atoms,alkyl alkanoates having 1 to 15 carbon atoms, ketones having 1 to 15carbon atoms, and chlorinated hydrocarbons,

(2) separating said volatile liquid and said prepolymer particles whensaid particles have become characterized by a high degree ofcrystallinity, and

(3) heating said crystallized prepolymer particles in an enclosedpolymerization zone under a vacuum at from 5 C. to 80 C. below theirmelting point, whereby a linear polyester having an inherent viscosityof at least 0.7 and also at least 0.3 units greater than for theprepolymer is obtained within about three hours of commencing saidheating in said polymerization zone, said inherent viscosities beingmeasured at 25 C. with a 0.25 percent by weight solution of the polymerin a solvent composed of 60 percent phenol and 40 percenttetrachloroethane.

2. A process as defined by claim 1 wherein said volatile liquid is amember selected from the group consisting of tetrachloroethane,perchloroethylene, methylene chloride, carbon tetrachloride, chloroform,aqueous acetone, anhydrous acetone, methanol, ethanol, isopropanol, bu-

tanol, aqueous methanol, aqueous ethanol, aqueous isopropanol, aqueousbutanol, ethyl acetate, and butyl acetate, said aqueous liquidscontaining from 25 to percent by weight of water.

3. A process as defined by claim 1 wherein said volatile liquid is amixture of equal weights of acetone and water.

4. A process as defined by claim 1 wherein said volatile liquid isacetone.

5. A process as defined by claim 1 wherein said difunctionaldicarboxylic acid having a hexacarbocyclic nucleus is4,4-sulfonyldibenzoic acid.

6. A process as defined by claim 1 wherein said dibasic acid having ahexacarbocyclic nucleus is terephthalic acid.

7. A process as defined by claim 1 wherein said glycol is neopentylglycol.

8. A process as defined by claim 1 wherein said prepolymer is of4,4-sulfonyldibenzoic acid and neopentyl glycol.

9. A process as defined by claim 1 wherein said prepolymer is of4,4-sulfonyldibenzoic acid, isophthalic acid, and neopentyl glycol.

10. A process as defined by claim 1 wherein said prepolymer is of4,4-sulfonyldibenzoic acid, terephthalic acid, and neopentyl glycol.

References Cited UNITED STATES PATENTS 2,706,722 4/1955 Caldwell260-32.8 2,901,466 8/1959 Kibler et al 260-75 3,014,011 12/1961Zoetbrood 260-75 3,075,952 1/1963 Coover et al. 260-75 WILLIAM H. SHORT,Primary Examiner.

LOUISE P. QUAST, Examiner.

